CGRect in Swift 3 rotating with correct origin - ios

Question

I'm trying to rotate a line (thin rectangle) around its endpoint. I have it working fine, but step 2 is to shorten the line and have it still rotate around the endpoint (center of rotation).
// Create and add a colored square
var rod = UIView()
var countsteps = 0
var Mass = 1
var Radius = 1.00
let rectWidth = screenWidth * 0.5
let rectVertical = screenHeight * 0.5
let rectLeft = screenWidth * 0.5
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
// set background color to blue
rod.backgroundColor = UIColor(red: 145/255, green: 170/255, blue: 157/255, alpha: 1)
//rod Line
rod.frame = CGRect(x: rectLeft, y: rectVertical, width: 3, height: rectWidth)
// finally, add the square to the screen
self.view.addSubview(rod)
//Create Timer
_ = Timer.scheduledTimer(timeInterval: 0.1, target: self, selector: #selector(Acceleration.update), userInfo: nil, repeats: true)
}
func update() {
UIView.animate(withDuration: 0.1, animations: {
//Slope Line
let rectSize = CGFloat(self.Radius) * self.rectWidth / 100
let amountRotation = CGFloat(CGFloat(self.countsteps)/57.3)
let originPoint = CGPoint(x: 0,y: 0)
self.rod.layer.anchorPoint = originPoint
self.rod.transform = CGAffineTransform(rotationAngle: amountRotation)
self.countsteps = self.countsteps + 1
if (self.countsteps > 359) {
self.countsteps = 0
}
})
}
I tried adding this line:
self.rod.frame.size = CGSize(width: 3.00, height: rectSize)
But, that makes the box rotate while changing proportions around a different axis.

Answer 1

Try adding this line:
self.rod.layer.position = originPoint
so, your update func looks like:
func update() {
UIView.animate(withDuration: 0.1, animations: {
//Slope Line
let rectSize = CGFloat(self.Radius) * self.rectWidth / 100
let amountRotation = CGFloat(CGFloat(self.countsteps)/57.3)
let originPoint = CGPoint(x: 0,y: 0)
self.rod.layer.anchorPoint = originPoint
self.rod.layer.position = originPoint
self.rod.transform = CGAffineTransform(rotationAngle: amountRotation)
self.countsteps = self.countsteps + 1
if (self.countsteps > 359) {
self.countsteps = 0
}
})
}
I seriously recommend adding some color to layers and views background, with some alpha, it is quite useful to detect what the system is doing, like a visual debug.